An ultrasonic parametric loudspeaker has been used as a device with a high directivity that transmits sounds to a specific area. The ultrasonic parametric loudspeaker causes an energy transmitted by an ultrasonic sound wave to be converted into an audible sound in air due to non-linear characteristics, thus making it audible. If one wishes to make the direction of transmission of the sound variable, there is required a large-scale mechanism of such as inclining mechanically the sound generating surface.
With respect to these issues, for example, Patent Documents 1 and 2 disclose technical arts. Patent Document 1 discloses the technical art in which an AD converter samples a modulation signal, which is used to amplitude-modulate an ultrasonic sound wave, with a predetermined sampling frequency, to generate sequentially a sample of modulation signal, the sample of modulation signal as generated is stored by a storage unit, a readout unit reads-out a plurality of samples having predetermined time periods, of the sample of modulation signal, from the storage unit, an ultrasonic sound wave oscillator oscillates the ultrasonic sound wave signal, a plurality of amplitude modulators amplitude-modulates the ultrasonic sound wave signal with the use of a plurality of samples as read-out, to output a plurality of modulated signals, and a plurality of electro-acoustic converters is operated by the plurality of modulated signals.
Patent Document 2 discloses the technical art in which a sample generator generates sequentially a sample of modulated signal in which an ultrasonic sound wave signal has been amplitude-modulated with the modulation signal, the sample of modulated signal as generated is stored by a storage unit, a readout unit reads-out a plurality of samples having predetermined time periods, of the sample of modulation signal, from the storage unit, and a plurality of electro-acoustic converters is operated respectively by the plurality of samples.